Oral or nasal delivery of a medicament using an inhalation device is a particularly attractive method of drug administration as these devices are relatively easy for a patient to use discreetly and in public. As well as delivering medicament to treat local diseases of the airway and other respiratory problems, they have more recently also been used to deliver drugs to the bloodstream via the lungs, thereby avoiding the need for hypodermic injections.
It is common for dry powder formulations to be pre-packaged in individual doses, usually in the form of capsules or blisters which each contain a single dose of the powder which has been accurately and consistently measured. A blister is generally cold formed from a ductile foil laminate or a plastics material and includes a puncturable lid which is permanently heat-sealed around the periphery of the blister during manufacture and after the dose has been introduced into the blister. A foil blister is preferred over capsules as each dose is protected from the ingress of water and penetration of gases such as oxygen in addition to being shielded from light and UV radiation all of which can have a detrimental effect on the delivery characteristics of the inhaler if a dose becomes exposed to them. Therefore, a blister offers excellent environmental protection to each individual drug dose.
Inhalation devices that receive a blister pack comprising a number of blisters each of which contain a pre-metered and individually packaged dose of the drug to be delivered are known. Actuation of the device causes a mechanism to breach or rupture a blister, such as by puncturing it or peeling the lid off, so that when the patient inhales, air is drawn through the blister entraining the dose therein that is then carried out of the blister through the device and via the patient's airway down into the lungs. Pressurized air or gas or other propellants may also be used to carry the dose out of the blister. Alternatively, the mechanism that punctures or opens the blister may push or eject the dose out of the blister into a receptacle from which the dose may subsequently be inhaled.
It is advantageous for the inhaler to be capable of holding a number of doses to enable it to be used repeatedly over a period of time without the requirement to open and/or insert a blister into the device each time it is used. Therefore, many conventional devices include means for storing a number of blisters each containing an individual dose of medicament. When a dose is to be inhaled, an indexing mechanism moves a previously emptied blister away from the opening mechanism so that a fresh one is moved into a position ready to be opened for inhalation of its contents.
An inhaler of the type described above is known from the Applicant's own co-pending international application no. PCT/GB2004/004416 filed on 18 Oct. 2004 and claiming priority from GB0324358.1 filed 17 Oct. 2003. This international application has been published as WO2005/037353 A1.
According to one embodiment described and claimed in WO 2005/037353 A1, and illustrated in FIGS. 1 and 2 of the accompanying drawings, an inhaler 1 has a housing 2 containing a coiled strip 3. The strip 3 has a plurality of individually spaced moisture proof blisters each containing a pre-measured dose of powdered medicament for inhalation. Each blister of the strip comprises a generally hemispherically shaped pocket and a flat puncturable lid permanently heat sealed to the pocket to hermetically seal the dose therein. The strip is preferably manufactured from foil laminate or a combination of foil laminate, such as aluminium, and plastics material.
An indexing mechanism 4 comprising a single actuating lever 5 unwinds the coil 3 one blister at a time so that they pass over a blister locating chassis 6 and successively through a blister piercing station 7, when the actuator 5 is pivoted in a direction indicated by arrow “A” in FIG. 2. The blister 3a located at the blister piercing station 7 on each movement of the actuator 5 is pierced on the return stroke of the actuator 5 (in the direction indicated by arrow “B” in FIG. 2) by piercing elements 8 on the actuator 5 itself so that, when a user inhales through a mouthpiece 9, an airflow is generated within the blister 3a to entrain the dose contained therein and carry it out of the blister 3a via the mouthpiece 9 and into the user's airway.
In another embodiment disclosed in WO2005/037353 A1, indexing and piercing of a blister positioned at the blister piercing station 7 is carried out in response to rotation of a cap that covers the mouthpiece in a closed position, rather than as a result of direct rotation of the actuator by the user.
Each of the devices disclosed in WO2005/037353 A1 have a drive mechanism that includes an indexing wheel. A blister strip passes over the indexing wheel and the wheel rotates in response to pivotal movement of an acutator or cap so as to drive or index the strip through the device. The drive mechanism is configured such that the indexing wheel rotates in response to rotation of the actuator or cap in one direction but remains stationary when the actuator or cap is rotated in the opposite direction.